It is known that the polymerization of olefins e.g. ethylene, especially by a gas phase polymerization process, involves the polymerization of olefin monomer with the aid of catalyst and optionally, if required depending on the used catalyst, a co-catalyst. Suitable catalysts for use in the production of polyolefins, and in particular for the preparation of polyethylene, comprise chromium-type catalysts, Ziegler-Natta catalysts and metallocene catalysts.
U.S. Pat. No. 3,726,845 describes the supply and control of the amount of catalyst and the maintenance of the catalyst line and pump free by alternately feeding catalyst slurry and diluent to the reaction zone.
It is well known that the polymerization reaction is quite sensitive to the quantity of catalyst utilized. It is important to control catalyst flow to a reactor since unexpected or uncontrolled catalyst injection in a reactor could lead to reactions that exceed cooling capacity of the reactor.
However, one of the major problems in the injection of catalyst to a reactor in prior art methods is that it is difficult to control the amount of catalyst and the flow rate of the catalyst injected.
It is an object of the present invention to provide for a method for the delivery of catalyst to a polymerization reactor wherein at least one of the above mentioned drawbacks is overcome.